This invention relates in general to nano electronic devices.
Important characteristics for a memory cell in electronic device are low cost, nonvolatility, high density, low power, and high speed. Conventional memory solutions include Read Only Memory (ROM), Programmable Read only Memory (PROM), Electrically Programmable Memory (EPROM), Electrically Erasable Programmable Read Only Memory (EEPROM), Dynamic Random Access Memory (DRAM) and Static Random Access Memory (SRAM).
ROM is relatively low cost but cannot be rewritten. PROM can be electrically programmed but with only a single write cycle. EPROM has read cycles that are fast relative to ROM and PROM read cycles, but has relatively long erase times and reliability only over a few iterative read/write cycles. EEPROM (or “Flash”) is inexpensive, and has low power consumption but has long write cycles (ms) and low relative speed in comparison to DRAM or SRAM. Flash also has a finite number of read/write cycles leading to low long-term reliability. ROM, PROM, EPROM and EEPROM are all non-volatile, meaning that if power to the memory is interrupted the memory will retain the information stored in the memory cells.
DRAM stores charge on transistor gates that act as capacitors but must be electrically refreshed every few milliseconds complicating system design by requiring separate circuitry to “refresh” the memory contents before the capacitors discharge. SRAM does not need to be refreshed and is fast relative to DRAM, but has lower density and is more expensive relative to DRAM. Both SRAM and DRAM are volatile, meaning that if power to the memory is interrupted the memory will lose the information stored in the memory cells.
Consequently, existing technologies are either non-volatile but are not randomly accessible and have low density, high cost, and limited ability to allow multiples writes with high reliability of the circuit's function, or they are volatile and complicate system design or have low density. Some emerging technologies have attempted to address these shortcomings.
For example, magnetic RAM (MRAM) or ferromagnetic RAM (FRAM) utilizes the orientation of magnetization or a ferromagnetic region to generate a nonvolatile memory cell. MRAM utilizes a magnetoresistive memory element involving the anisotropic magnetoresistance or giant magnetoresistance of ferromagnetic materials yielding nonvolatility. Both of these types of memory cells have relatively high resistance and low-density. A different memory cell based upon magnetic tunnel junctions has also been examined but has not led to large-scale commercialized MRAM devices. FRAM uses a circuit architecture similar to DRAM but which uses a thin film ferroelectric capacitor. This capacitor is purported to retain its electrical polarization after an externally applied electric field is removed yielding a nonvolatile memory. FRAM suffers from a large memory cell size, and it is difficult to manufacture as a large-scale integrated component. More details are discussed in U.S. Pat. Nos. 4,853,893; 4,888,630; and 5,198,994, the contents of which are incorporated by reference.
Another technology having non-volatile memory is phase change memory. This technology stores information via a structural phase change in thin-film alloys incorporating elements such as selenium or tellurium. These alloys are purported to remain stable in both crystalline and amorphous states allowing the formation of a bistable switch. While the nonvolatility condition is met, this technology appears to suffer from slow operations, difficulty of manufacture and reliability and has not reached a state of commercialization. More details are discussed in U.S. Pat. Nos. 3,448,302; 4,845,533; 4,876,667; 6,044,008, the contents of which are incorporated by reference.
Wire crossbar memory (MWCM) has also been disclosed in U.S. Pat. Nos. 6,128,214; 6,159,620; and 6,198,655, the contents of which are incorporated by reference. These memory proposals envision molecules as bistable switches. Two wires (either a metal or semiconducting type) have a layer of molecules or molecule compounds sandwiched in between. Chemical assembly and electrochemical oxidation or reduction are used to generate an “on” or “off” state. This form of memory requires highly specialized wire junctions and may not retain nonvolatility owing to the inherent instability found in redox processes. Memory devices have been proposed which use nanoscopic wires, such as single-walled carbon nanotubes, to form crossbar junctions to serve as memory cells. Typically, individual single-walled nanotube wires suspended over other wires define memory cells. Electrical signals are written to one or both wires to cause them to physically attract or repel relative to one another. Each physical state (i.e., attracted or repelled wires) corresponds to an electrical state. Repelled wires are an open circuit junction. Attracted wires are a closed state forming a rectified junction. When electrical power is removed from the junction, the wires retain their physical (and thus electrical) state thereby forming a non-volatile memory cell.
In a parallel trend, as discussed in United States Patent Application 20030121764, nanowires are often thin strands of conductive or semiconductive materials with diameters in the nanometer range to a few hundred nanometers. The nanowires have been operated in a room-temperature, ultraviolet lasing mode. These devices can convert electrical energy into light energy. United States Patent Application 20050009224 mentions the high cost of manufacturing conventional solar cells limits their widespread use as a source of power generation. The construction of conventional silicon solar cells involves four main processes: the growth of the semiconductor material, separation into wafers, formation of a device and its junctions, and encapsulation. For cell fabrication alone, numerous steps are required to make the solar cell and many of these steps require high temperatures (300° C.-1000° C.), high vacuum or both. In addition, the growth of the semiconductor from a melt is at temperatures above 1400° C. under an inert argon atmosphere. To obtain high efficiency devices (>10%), structures involving concentrator systems to focus sunlight onto the device, multiple semiconductors and quantum wells to absorb more light, or higher performance semiconductors such as GaAs and InP, are needed. These options all result in increased costs.
Recently, advances in textile technology have resulted in improved fabrics and textiles. For example, U.S. Pat. No. 6,821,936 discloses that silver-containing inorganic microbiocides can be utilized as antimicrobial agents on and within a plethora of different substrates and surfaces. In particular, such microbiocides have been adapted for incorporation within melt spun synthetic fibers in order to provide certain fabrics which selectively and inherently exhibit antimicrobial characteristics. Furthermore, attempts have been made to apply such specific microbiocides on the surfaces of fabrics and yarns with little success from a durability standpoint. A topical treatment with such compounds has never been successfully applied as a durable finish or coating on a fabric or yarn substrate. Although such silver-based agents provide excellent, durable, antimicrobial properties, to date such is the sole manner available within the prior art of providing a long-lasting, wash-resistant, silver-based antimicrobial textile. However, such melt spun fibers are expensive to make due to the large amount of silver-based compound required to provide sufficient antimicrobial activity in relation to the migratory characteristics of such a compound within the fiber itself to its surface. A topical coating is also desirable for textile and film applications, particularly after finishing of the target fabric or film.
Such a topical procedure permits treatment of a fabric's individual fibers prior to or after weaving, knitting, and the like, in order to provide greater versatility to the target yarn without altering its physical characteristics. Such a coating, however, must prove to be wash durable, particularly for apparel fabrics, in order to be functionally acceptable. Furthermore, in order to avoid certain problems, it is highly desirable for such a metallized treatment to be electrically non-conductive on the target fabric, yarn, and/or film surface. The '936 patent applies a treatment with silver ions, particularly as constituents of inorganic metal salts or zeolites in the presence of a resin binder, either as a silver-ion overcoat or as a component of a dye bath mixture admixed with the silver-ion antimicrobial compound.
United States Patent Application 20040142168 discloses fibers, and fabrics produced from the fibers, are made water repellent, fire-retardant and/or thermally insulating by filling void spaces in the fibers and/or fabrics with a powdered material. When the powder is sufficiently finely divided, it clings to the fabric's fibers and to itself, resisting the tendency to be removed from the fabric.